One solution to the problem of dependence on foreign sources for energy, particularly for fuel for motor vehicles, is converting biomass to ethanol. The presently available processes use corn (maize) or other starch-containing biomass.
For efficiency, the process must convert a large percentage of the biomass to ethanol. The process should proceed rapidly so that the plant can produce the maximum amount of ethanol per unit time.
Corn is one preferred substance used for ethanol production. As is well known, corn kernels comprise a germ portion and a carbohydrate portion. The germ portion comprises about 8% of the entire weight. The germ contains about 40% by weight of valuable corn oil as well as some carbohydrates and fiber. The carbohydrate portion comprises starch, sugar, and fiber, and contains almost no oil. On a weight basis, corn kernels are about 6-7% oil, 60-70% carbohydrates, 20-25% fiber, and 10-12% water.
An efficient ethanol process uses enzymes to convert starches in the biomass to sugar before the fermentation. The process ferments sugars of any kind to produce CO2 and the ethanol, but cannot convert starch to ethanol. Since CO2 is a greenhouse gas, the less CO2 produced, the better.
In current corn ethanol processes, corn is ground and mixed with a solvent to form a ground corn slurry. This slurry comprises both the germ and the carbohydrate portions. Enzymes added to the slurry convert the starch to sugar. Fermenting the sugar in the slurry then produces ethanol. A distillation step separates the ethanol from the slurry. The ethanol is then further refined to a form useable as automobile fuel.
The common ethanol production process has a number of problems. One is lack of efficiency. It turns out that the sum of all of the energy inputs needed to produce a unit measure of corn is not much less than the energy content of the ethanol provided by that unit measure. Of course, the ethanol process does produce some useful by-products, such as animal feed and the corn oil usable in plastic manufacture. But overall, current ethanol production processes are not outstandingly efficient.
Secondly, the current ethanol processes produces more contaminating fusel oil in the distilled ethanol than desirable. Fusel oil is an aromatic alcohol that reduces speed and efficiency in the distillation step. The fusel oil is a byproduct of corn oil that reaches the fermenting tank. Accordingly, removing as much corn oil as possible from the ground corn slurry reduces the concentration of the fusel oil.